Never mind the World Cup, you know summer is underway when you see online stores start their big summer sales. You're going to have to keep checking GOG.com on a regular basis as it's got some daily deals and bundles, mixed in with plenty of flash sales. Whilst GOG.com's catalog of games isn't the biggest, it's still a great place to get plenty of DRM-free titles, especially now that the site is releasing indie games.
At the time of writing, there's a fantastic D&D bundle which includes Baldur's Gate and Planescape Torment that costs just $21.10 and another bundle containing the Rollercoaster Tycoon series for $8.97. There's almost no point trying to list what the current deals are right now, as the flash deals are changing every 30 minutes but I'd advise you keep an eye out for some of the more recent indie releases like The Swapper or FRACT OSC.